I actually just installed Windows 7 64 bit on Fusion this morning. Gave it 1.8gb of ram with 2 virtual processors. Runs great and is speedy. Only issue I noticed was trying to run solitaire in unity....it kept closing on me. Not sure of the reason but it worked with other things like minesweeper and IE.
I haven't tried the other vm programs but i think fusion is running great. Btw, I chose fusion because it had 64 bit support while parallels doesn't (I think).